1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to a disk drive comprising a hub ratchet arm disengaged through angular velocity.
2. Description of the Prior Art
The spindle motor within a disk drive typically employs high accuracy, low noise spindle bearing balls encased in lubricating and anti-rust oils. During shipping, vibrations may cause the spindle bearing balls to oscillate in small back and forth motions causing the bearing balls to push through the lubricating and anti-rust oils until there is metal-on-metal contact. The metal-on-metal contact creates micro spots of fretting corrosion which exacerbates acoustic noise and non-repeatable run-out (NRRO).
There is, therefore, a need for a disk drive which minimizes metal-on-metal contact of the spindle bearing balls due to vibrations during shipping.
The present invention may be regarded as a disk drive comprising a disk, a head actuated radially over the disk, and a spindle motor for rotating the disk. The spindle motor comprises a stator, a spindle shaft, and a hub rotated by the stator about the spindle shaft and forming a cylindrical cavity with respect to the spindle shaft, the hub comprising a ratchet arm engaging at least one of the spindle shaft and stator. The ratchet arm disengages from the at least one of the spindle shaft and stator due to the hub rotating at an angular velocity greater than a threshold.
In one embodiment, the ratchet arm applies a first frictional force to the at least one of the spindle shaft and stator while the hub is rotating in a first direction, and the ratchet arm applies a second frictional force while the hub attempts to rotate in a second direction opposite the first direction, wherein the second frictional force is greater than the first frictional force. In one embodiment, the ratchet arm comprises a wing member having a distal end for engaging the hub when the hub attempts to rotate in the second direction.
In one embodiment, the ratchet arm disengages from the spindle shaft due to centrifugal force while the hub is rotating at the angular velocity greater than the threshold. In an alternative embodiment, the ratchet arm disengages from the at least one of the spindle shaft and stator due to an air bearing forming between the ratchet arm and the at least one of the spindle shaft and stator while the hub is rotating at the angular velocity greater than the threshold. In yet another embodiment, the ratchet arm disengages from the at least one of the spindle shaft and stator due to windage pushing the ratchet arm away from the at least one of the spindle shaft and stator while the hub is rotating at the angular velocity greater than the threshold.
In one embodiment, the ratchet arm is formed by bending a tab off a rectangular piece of sheet metal, and wrapping the rectangular piece of sheet metal into a cylinder wherein the tab extends into an interior of the cylinder. The cylinder is inserted over the spindle shaft and attached to the hub, wherein the tab engages the spindle shaft.
The present invention may also be regarded as a spindle motor comprising a stator, a spindle shaft, and a hub rotated by the stator about the spindle shaft and forming a cylindrical cavity with respect to the spindle shaft. The hub comprises a ratchet arm engaging at least one of the spindle shaft and stator. The ratchet arm disengages from the at least one of the spindle shaft and stator due to the hub rotating at an angular velocity greater than a threshold.
The present invention may also be regarded as a disk drive comprising a disk, a head actuated radially over the disk, and a spindle motor for rotating the disk. The spindle motor comprises a stator, a spindle shaft, a ratchet arm connected to at least one of the spindle shaft and stator, and a hub rotated by the stator about the spindle shaft and forming a cylindrical cavity with respect to the spindle shaft. The ratchet arm engages the hub when the hub is not rotating, and the ratchet arm disengages from the hub due to the hub rotating at an angular velocity greater than a threshold.
The present invention may also be regarded as a spindle motor comprising a stator, a spindle shaft, a ratchet arm connected to at least one of the spindle shaft and stator, and a hub rotated by the stator about the spindle shaft and forming a cylindrical cavity with respect to the spindle shaft. The ratchet arm engages the hub when the hub is not rotating, and the ratchet arm disengages from the hub due to the hub rotating at an angular velocity greater than a threshold.